This invention relates to exercise apparatus of the type in which (a) the exercise force on a user-operated member produces a substantially linear force which requires conversion into a rotary driving torque, and (b) the user-operated member is returned to a given position by an automatic retraction force. The primary example of such an exercise apparatus is one which simulates stair climbing
In common assignee application Ser. No. 289,563, filed Dec. 23, 1988, and also in Pat. No. 4,708,338, referred to in the "Background" portion of Ser. No. 289,563, an apparatus is described having two foot pedals which cause rotation of a torque transmission member under the weight of the user as such weight is alternately placed on each pedal, driving it from its upper position to its lower position. There are, essentially, two portions of the force-transmitting system in such an apparatus. The first portion converts the downward pressure on each pedal into a one-way torque which turns a large diameter sprocket wheel. The second portion conveys the torque from the large diameter sprocket wheel to a small diameter sprocket wheel, which is on a shaft driving a variable resistance brake.
In the apparatus described above, each portion of the force transmitting system comprises sprocket wheels and a roller, or sprocket, chain. The pin-supported rollers on each roller chain mesh with teeth of the sprocket wheel(s), providing a positive (non-slipping) force-transmitting connection. The first portion of the force transmitting system comprises, at each pedal, a roller chain which is connected at one end to the pedal, which engages a sprocket wheel, and which is connected at the other end to an anchored retracting spring Each pedal-driven sprocket wheel operates through a one-way roller clutch to convert downward pressure on the pedal into torque rotating a shaft in a single direction. The shaft drives the large diameter sprocket wheel of the second portion of the force transmitting system.
Although the larger and smaller sprocket wheels and roller chain in the second portion of the force-transmitting system have functioned successfully, the sprocket chain connecting the pedal to the return spring has exhibited serious tendencies to break under operating stress. In other words, lack of durability of this roller chain has been a significant source of apparatus breakdowns, necessitating parts replacement and causing substantial down time of the apparatus.
It appears that many of such roller chain failures are caused by lateral stresses on the links of the chain, which are not designed to resist significant lateral forces. Any misalignment between portions of the chain adds such lateral bending stress to the tension force for which the chains are designed.
Also erosion (excessive wear) of the chain elements appears to be a factor. Whereas the roller chain in the second portion of the force-transmitting system is fully covered and protected by a shroud, such protection of the roller chain in the first portion of the force-transmitting system is impossible, because the pedal-connected end of each chain is exposed Various eroding substances, such as dirt adhering to the greased chain elements, or perspiration of the users, are inevitably collected on the chain elements.
Another source of potential failure in the sprocket wheel/roller chain combination is "freezing-up", or locking, of chain connecting pins, due to contaminating substances. Such locking can cause breakage of sprocket wheel teeth, because the chain does not properly engage the sprocket teeth.
Particularly in cases where stair climbers, or similarly operated exercise devises, are used in fitness clubs, durability is a major requirement And the inability of a device to operate due to sprocket chain or sprocket wheel failure creates significant annoyances.